Differential modulation of late sodium current by protein kinase A in R1623Q mutant of LQT3

Abstract

Aims-In the type 3 long QT syndrome (LQT3), shortening of the QT interval by overdrive pacing is used to prevent life-threatening arrhythmias. However, it is unclear whether accelerated heart rate induced by β-adrenergic agents produces similar effects on the late sodium current (I Na ) to those by overdrive pacing therapy. We analyzed the β-adrenergic-like effects of protein kinase A and fluoride on I Na in R1623Q mutant channels.Main methods-cDNA encoding either wild-type (WT) or R1623Q mutant of hNa v 1.5 was stably transfected into HEK293 cells. I Na was recorded using a whole-cell patch-clamp technique at 23 °C .Key findings-In R1623Q channels, 2 mM pCPT-AMP and 120 mM fluoride significantly delayed macroscopic current decay and increased relative amplitude of the late I Na in a time-dependent manner. Modulations of peak I Na gating kinetics (activation, inactivation, recovery from inactivation) by fluoride were similar in WT and R1623Q channels. The effects of fluoride were almost completely abolished by concomitant dialysis with a protein kinase inhibitor. We also compared the effect of pacing with that of β-adrenergic stimulation by analyzing the frequency-dependence of the late I Na . Fluoride augmented frequency-dependent reduction of the late I Na , which was due to preferential delay of recovery of late I Na . However, the increase in late I Na by fluoride at steady-state was more potent than the frequency-dependent reduction of late I Na .Significance-Different basic mechanisms participate in the QT interval shortening by pacing and β-adrenergic stimulation in the LQT3.

Enhanced fast-inactivated state stability of cardiac sodium channels by a novel voltage sensor SCN5A mutation, R1632C, as a cause of atypical Brugada syndrome

“…R1632C I Na availability in both the atrium and the ventricle, whose resting membrane potentials are approximately À90 mV, is likely to be substantially reduced (Online Supplemental Figure S2), although the current reduction caused by the hyperpolarizing shift in voltage dependence of inactivation might be enhanced in our experimental condition. 28 A pronounced reduction of I Na in both the atrium and the ventricle may be associated with multiple electrophysiological phenotypes (BrS, AT, and SND) observed in our patient. An increased HV interval and QRS duration could also be attributable to the R1632C mutation.…”

“…Of note, repetitive depolarizing pulses rapidly attenuated R1632C I Na compared with WT I Na (Online Supplemental Figures S3B and S3C), and β-adrenergic stimulation augments the frequency-dependent reduction of I Na . 28 These findings may explain the clinical phenotypes of our patient such that AT preferentially occurred during exercise or was induced by high-frequency atrial stimuli during isoproterenol infusion.…”

“…Currents were acquired at 20-50 kHz and low-pass filtered at 5 kHz using an analog-to-digital interface (Digidata 1440A acquisition system, Molecular Devices). To avoid the possible time-dependent shift of activation and steady-state inactivation curves, 28 all pulse protocols were applied more than 5 minutes after membrane rupture. Therefore, the time-dependent shift became negligible.…”

Cardiac sodium channel mutation associated with epinephrine-induced QT prolongation and sinus node dysfunction

“…PKA stimulation has also been reported to augment late Na + currents in mutant Na + channels (ΔKPQ, D1790G and R1623Q). [22][23][24] One of these three SCN5A mutations, D1790G, is located in the C-terminal domain. Its effect on the augmentation of late Na + currents was reportedly diminished by the co-presence of SCN5A-S36A and -S525A mutations, which lost phosphorylation sites in the N-terminus and in the cytoplasmic I-II loop, respectively.…”

Effects of late sodium current enhancement during LQT-related arrhythmias. A simulation study

“…The g NaL was fitted by Tsurugi et al [16] and Maltsev et a experiments, they measured an I NaL /I NaF approximately, and g NaL was fitted in our m The conductance yielded 0.055 mS/µF. It i the ratio does not change with temperature experimental data demonstrated that the inactivation is modified by temperature, fo multiplied τ h by the factor Q10 (2.2), so τ h y 37ºC [8;18].…”